GLPIXELTRANSFER

NAME

glPixelTransferf, glPixelTransferi
- set pixel transfer modes

C SPECIFICATION

void glPixelTransferf(
GLenum pname,

GLfloat param )

void glPixelTransferi(
GLenum pname,

GLint param )

delim $$

PARAMETERS

pname

Specifies the symbolic name of the pixel transfer parameter to be set.
Must be one of the following:
GL_MAP_COLOR,
GL_MAP_STENCIL,
GL_INDEX_SHIFT,
GL_INDEX_OFFSET,
GL_RED_SCALE,
GL_RED_BIAS,
GL_GREEN_SCALE,
GL_GREEN_BIAS,
GL_BLUE_SCALE,
GL_BLUE_BIAS,
GL_ALPHA_SCALE,
GL_ALPHA_BIAS,
GL_DEPTH_SCALE, or
GL_DEPTH_BIAS.

DESCRIPTION

glPixelTransfer sets pixel transfer modes that affect the operation of subsequent
glCopyPixels,
glCopyTexImage1D,
glCopyTexImage2D,
glCopyTexSubImage1D,
glCopyTexSubImage2D,
glCopyTexSubImage3D,
glDrawPixels,
glReadPixels,
glTexImage1D,
glTexImage2D,
glTexImage3D,
glTexSubImage1D,
glTexSubImage2D, and
glTexSubImage3D commands.
Additionally, if the GL_ARB_imaging subset is supported, the
routines
glColorTable,
glColorSubTable,
glConvolutionFilter1D,
glConvolutionFilter2D,
glHistogram,
glMinmax, and
glSeparableFilter2D are also affected.
The algorithms that are specified by pixel transfer modes operate on
pixels after they are read from the frame buffer
(glCopyPixelsglCopyTexImage1D,
glCopyTexImage2D,
glCopyTexSubImage1D,
glCopyTexSubImage2D,
glCopyTexSubImage3D, and
glReadPixels),
or unpacked from client memory
(glDrawPixels, glTexImage1D, glTexImage2D, glTexImage3D,
glTexSubImage1D, glTexSubImage2D, and glTexSubImage3D).
Pixel transfer operations happen in the same order,
and in the same manner,
regardless of the command that resulted in the pixel operation.
Pixel storage modes
(see glPixelStore)
control the unpacking of pixels being read from client memory,
and the packing of pixels being written back into client memory.

Pixel transfer operations handle four fundamental pixel types:
color,
color index,
depth, and
stencil.
Color pixels consist of four floating-point values
with unspecified mantissa and exponent sizes,
scaled such that 0 represents zero intensity
and 1 represents full intensity.
Color indices comprise a single fixed-point value,
with unspecified precision to the right of the binary point.
Depth pixels comprise a single floating-point value,
with unspecified mantissa and exponent sizes,
scaled such that 0.0 represents the minimum depth buffer value,
and 1.0 represents the maximum depth buffer value.
Finally,
stencil pixels comprise a single fixed-point value,
with unspecified precision to the right of the binary point.

The pixel transfer operations performed on the four basic pixel types are
as follows:

Color

Each of the four color components is multiplied by a scale factor,
then added to a bias factor.
That is,
the red component is multiplied by GL_RED_SCALE,
then added to GL_RED_BIAS;
the green component is multiplied by GL_GREEN_SCALE,
then added to GL_GREEN_BIAS;
the blue component is multiplied by GL_BLUE_SCALE,
then added to GL_BLUE_BIAS; and
the alpha component is multiplied by GL_ALPHA_SCALE,
then added to GL_ALPHA_BIAS.
After all four color components are scaled and biased,
each is clamped to the range [0,1].
All color, scale, and bias values are specified with glPixelTransfer.

If GL_MAP_COLOR is true,
each color component is scaled by the size of the corresponding
color-to-color map,
then replaced by the contents of that map indexed by the scaled component.
That is,
the red component is scaled by GL_PIXEL_MAP_R_TO_R_SIZE,
then replaced by the contents of GL_PIXEL_MAP_R_TO_R indexed by itself.
The green component is scaled by GL_PIXEL_MAP_G_TO_G_SIZE,
then replaced by the contents of GL_PIXEL_MAP_G_TO_G indexed by itself.
The blue component is scaled by GL_PIXEL_MAP_B_TO_B_SIZE,
then replaced by the contents of GL_PIXEL_MAP_B_TO_B indexed by itself.
And
the alpha component is scaled by GL_PIXEL_MAP_A_TO_A_SIZE,
then replaced by the contents of GL_PIXEL_MAP_A_TO_A indexed by itself.
All components taken from the maps are then clamped to the range [0,1].
GL_MAP_COLOR is specified with glPixelTransfer.
The contents of the various maps are specified with glPixelMap.

If the GL_ARB_imaging extension is supported, each of the four
color components may be scaled and biased after transformation by the
color matrix.
That is,
the red component is multiplied by GL_POST_COLOR_MATRIX_RED_SCALE,
then added to GL_POST_COLOR_MATRIX_RED_BIAS;
the green component is multiplied by GL_POST_COLOR_MATRIX_GREEN_SCALE,
then added to GL_POST_COLOR_MATRIX_GREEN_BIAS;
the blue component is multiplied by GL_POST_COLOR_MATRIX_BLUE_SCALE,
then added to GL_POST_COLOR_MATRIX_BLUE_BIAS; and
the alpha component is multiplied by GL_POST_COLOR_MATRIX_ALPHA_SCALE,
then added to GL_POST_COLOR_MATRIX_ALPHA_BIAS.
After all four color components are scaled and biased,
each is clamped to the range [0,1].

Similiarly, if the GL_ARB_imaging extension is supported, each of
the four color components may be scaled and biased after processing by
the enabled convolution filter.
That is,
the red component is multiplied by GL_POST_CONVOLUTION_RED_SCALE,
then added to GL_POST_CONVOLUTION_RED_BIAS;
the green component is multiplied by GL_POST_CONVOLUTION_GREEN_SCALE,
then added to GL_POST_CONVOLUTION_GREEN_BIAS;
the blue component is multiplied by GL_POST_CONVOLUTION_BLUE_SCALE,
then added to GL_POST_CONVOLUTION_BLUE_BIAS; and
the alpha component is multiplied by GL_POST_CONVOLUTION_ALPHA_SCALE,
then added to GL_POST_CONVOLUTION_ALPHA_BIAS.
After all four color components are scaled and biased,
each is clamped to the range [0,1].

Color index

Each color index is shifted left by GL_INDEX_SHIFT bits; any bits
beyond the number of fraction bits carried
by the fixed-point index are filled with zeros.
If GL_INDEX_SHIFT is negative,
the shift is to the right,
again zero filled.
Then GL_INDEX_OFFSET is added to the index.
GL_INDEX_SHIFT and GL_INDEX_OFFSET are specified with
glPixelTransfer.

From this point, operation diverges depending on the required of
the resulting pixels.
If the resulting pixels are to be written to a color index buffer,
or if they are being read back to client memory in GL_COLOR_INDEX ,
the pixels continue to be treated as indices.
If GL_MAP_COLOR is true,
each index is masked by $2 sup n ~-~ 1$,
where $n$ is GL_PIXEL_MAP_I_TO_I_SIZE,
then replaced by the contents of GL_PIXEL_MAP_I_TO_I indexed by the
masked value.
GL_MAP_COLOR is specified with glPixelTransfer.
The contents of the index map is specified with glPixelMap.

If the resulting pixels are to be written to an RGBA color buffer,
or if they are read back to client memory in a other than
GL_COLOR_INDEX,
the pixels are converted from indices to colors by referencing the
four maps
GL_PIXEL_MAP_I_TO_R,
GL_PIXEL_MAP_I_TO_G,
GL_PIXEL_MAP_I_TO_B, and
GL_PIXEL_MAP_I_TO_A.
Before being dereferenced,
the index is masked by $2 sup n ~-~ 1$,
where $n$ is
GL_PIXEL_MAP_I_TO_R_SIZE for the red map,
GL_PIXEL_MAP_I_TO_G_SIZE for the green map,
GL_PIXEL_MAP_I_TO_B_SIZE for the blue map, and
GL_PIXEL_MAP_I_TO_A_SIZE for the alpha map.
All components taken from the maps are then clamped to the range [0,1].
The contents of the four maps is specified with glPixelMap.

Depth

Each depth value is multiplied by GL_DEPTH_SCALE,
added to GL_DEPTH_BIAS,
then clamped to the range [0,1].

Stencil

Each index is shifted GL_INDEX_SHIFT bits just as a color index is,
then added to GL_INDEX_OFFSET.
If GL_MAP_STENCIL is true,
each index is masked by $2 sup n ~-~ 1$,
where $n$ is GL_PIXEL_MAP_S_TO_S_SIZE,
then replaced by the contents of GL_PIXEL_MAP_S_TO_S indexed by the
masked value.

The following table gives the type,
initial value,
and range of valid values for each of the pixel transfer parameters
that are set with glPixelTransfer.

pname

Type

Initial Value

Valid Range

GL_MAP_COLOR

boolean

false

true/false

GL_MAP_STENCIL

boolean

false

true/false

GL_INDEX_SHIFT

integer

0

(-∞,∞)

GL_INDEX_OFFSET

integer

0

(-∞,∞)

GL_RED_SCALE

float

1

(-∞,∞)

GL_GREEN_SCALE

float

1

(-∞,∞)

GL_BLUE_SCALE

float

1

(-∞,∞)

GL_ALPHA_SCALE

float

1

(-∞,∞)

GL_DEPTH_SCALE

float

1

(-∞,∞)

GL_RED_BIAS

float

0

(-∞,∞)

GL_GREEN_BIAS

float

0

(-∞,∞)

GL_BLUE_BIAS

float

0

(-∞,∞)

GL_ALPHA_BIAS

float

0

(-∞,∞)

GL_DEPTH_BIAS

float

0

(-∞,∞)

GL_POST_COLOR_MATRIX_RED_SCALE

float

1

(-∞,∞)

GL_POST_COLOR_MATRIX_GREEN_SCALE

float

1

(-∞,∞)

GL_POST_COLOR_MATRIX_BLUE_SCALE

float

1

(-∞,∞)

GL_POST_COLOR_MATRIX_ALPHA_SCALE

float

1

(-∞,∞)

GL_POST_COLOR_MATRIX_RED_BIAS

float

0

(-∞,∞)

GL_POST_COLOR_MATRIX_GREEN_BIAS

float

0

(-∞,∞)

GL_POST_COLOR_MATRIX_BLUE_BIAS

float

0

(-∞,∞)

GL_POST_COLOR_MATRIX_ALPHA_BIAS

float

0

(-∞,∞)

GL_POST_CONVOLUTION_RED_SCALE

float

1

(-∞,∞)

GL_POST_CONVOLUTION_GREEN_SCALE

float

1

(-∞,∞)

GL_POST_CONVOLUTION_BLUE_SCALE

float

1

(-∞,∞)

GL_POST_CONVOLUTION_ALPHA_SCALE

float

1

(-∞,∞)

GL_POST_CONVOLUTION_RED_BIAS

float

0

(-∞,∞)

GL_POST_CONVOLUTION_GREEN_BIAS

float

0

(-∞,∞)

GL_POST_CONVOLUTION_BLUE_BIAS

float

0

(-∞,∞)

GL_POST_CONVOLUTION_ALPHA_BIAS

float

0

(-∞,∞)

glPixelTransferf can be used to set any pixel transfer parameter.
If the parameter type is boolean,
0 implies false and any other value implies true.
If pname is an integer parameter,
param is rounded to the nearest integer.

Likewise,
glPixelTransferi can be used to set any of the
pixel transfer parameters.
Boolean parameters are set to false if param is 0 and to true otherwise.
param is converted to floating point before being assigned to real-valued parameters.

NOTES

If a
glColorTable,
glColorSubTable,
glConvolutionFilter1D,
glConvolutionFilter2D,
glCopyPixels,
glCopyTexImage1D,
glCopyTexImage2D,
glCopyTexSubImage1D,
glCopyTexSubImage2D,
glCopyTexSubImage3D,
glDrawPixels,
glReadPixels,
glSeparableFilter2D,
glTexImage1D,
glTexImage2D,
glTexImage3D,
glTexSubImage1D,
glTexSubImage2D, or
glTexSubImage3D.
command is placed in a display list
(see glNewList and glCallList),
the pixel transfer mode settings in effect when the display list is
executed
are the ones that are used.
They may be different from the settings when the command was compiled
into the display list.

ERRORS

GL_INVALID_ENUM is generated if pname is not an accepted value.

GL_INVALID_OPERATION is generated if glPixelTransfer
is executed between the execution of glBegin
and the corresponding execution of glEnd.

ASSOCIATED GETS

glGet with argument GL_MAP_COLORglGet with argument GL_MAP_STENCILglGet with argument GL_INDEX_SHIFTglGet with argument GL_INDEX_OFFSETglGet with argument GL_RED_SCALEglGet with argument GL_RED_BIASglGet with argument GL_GREEN_SCALEglGet with argument GL_GREEN_BIASglGet with argument GL_BLUE_SCALEglGet with argument GL_BLUE_BIASglGet with argument GL_ALPHA_SCALEglGet with argument GL_ALPHA_BIASglGet with argument GL_DEPTH_SCALEglGet with argument GL_DEPTH_BIASglGet with argument GL_POST_COLOR_MATRIX_RED_SCALEglGet with argument GL_POST_COLOR_MATRIX_RED_BIASglGet with argument GL_POST_COLOR_MATRIX_GREEN_SCALEglGet with argument GL_POST_COLOR_MATRIX_GREEN_BIASglGet with argument GL_POST_COLOR_MATRIX_BLUE_SCALEglGet with argument GL_POST_COLOR_MATRIX_BLUE_BIASglGet with argument GL_POST_COLOR_MATRIX_ALPHA_SCALEglGet with argument GL_POST_COLOR_MATRIX_ALPHA_BIASglGet with argument GL_POST_CONVOLUTION_RED_SCALEglGet with argument GL_POST_CONVOLUTION_RED_BIASglGet with argument GL_POST_CONVOLUTION_GREEN_SCALEglGet with argument GL_POST_CONVOLUTION_GREEN_BIASglGet with argument GL_POST_CONVOLUTION_BLUE_SCALEglGet with argument GL_POST_CONVOLUTION_BLUE_BIASglGet with argument GL_POST_CONVOLUTION_ALPHA_SCALEglGet with argument GL_POST_CONVOLUTION_ALPHA_BIAS